MEXICO CITY — Authorities in north-central Mexico say they are investigating four men found carrying a drone equipped with a powerful bomb and a remote-controlled detonator.

The chief prosecutor in Guanajuato state says federal police caught the four men in a car near the city of Salamanca late last week.

Prosecutor Carlos Zamarripa says the drone had “a big explosive charge.” An assault rifle was also found in the vehicle.

It was unclear where the men planned to detonate the drone.

Zamarripa says the men belonged to a “crime cell,” but refused to say which drug gang or cartel.

Guanajuato was spared much of the violence that hit other states during Mexico’s drug war, but has recently been hit by gangs that specialize in fuel thefts from government pipelines and train robberies.